Shares in YouGov slumped 4pc, a far heavier fall than the wider London market, and Paris-listed rival Ipsos slid 1.5pc following Hillary Clinton’s unexpected defeat, a result that had not been anticipated by most polls.

YouGov has been expanding in the US, which is now its biggest market, and in its last survey, with the Economist, released just before election day, had given Mrs Clinton a four-point lead over Mr Trump.